What has helped with mine is very methodically discussing what he needs to do for his wellness and setting up a to-do list together. Without it, he will act very similar with tech as your DS. It helps when we use the tech for other things and giving him something else to do. As a pp said, there needs to be a known replacement for the screens.
So, with my DS, one thing was he needs to do something physical. We discussed what type of fitness was he interested in, he wants to get faster, so now does the Couch-to-5k app 3-4 days a week first thing in the morning. We do similar with housework, homework (we use a pomodoro timer for this with this which has really helped), other studying (asking things he wanted to learn about, and now we have coding, an IT technician course, and similar as part of his routine), and so on. A lot of this also involves using tech, and often what doesn't use tech ends up having his phone as a music player, but it's helped to give him the structure he needs to handle the obsessive habits he can get into.
Socializing is taking more effort, he keeps liking ideas but not following through yet, and we have to have a backup when he's not well enough to do the things on his list. Last week, he was given the choice of heading back to bed or reading until lunch time because otherwise he would have just jumped on an electronic and I would have gotten annoyed about doing that if he's too unwell for anything on his list, but it has made major improvements.
Also, him agreeing to use Google Family Link to track what apps he's using and for how long. Whenever he gets new phone game, I give him a week, and then we look through the time used and decide whether he needs external support through the app to help him to do other things. He's only needed it on a couple (youtube being one of them, but I assure him that that is a rabbithole for many people, these things are designed to be this way).
My oldest has been significantly stronger than me since he was 12, so I entirely get how bad it can get. It sounds really rough, but also something a lot of us have dealt with so I hope some of the advice on this thread can help.